It's certainly possible to develop on a Windows machine, in fact, my first application was exclusively developed on the old Dell Precision I had at the time :)
There are three routes;
- Install OSx86 (aka iATKOS / Kalyway) on a second partition/disk and dual boot.
- Run Mac OS X Server under VMWare (Mac OS X 10.7 (Lion) onwards, read the update below).
- Use Delphi XE4 and the macincloud service. This is a commercial toolset, but the component and lib support is growing.
The first route requires modifying (or using a pre-modified) image of Leopard that can be installed on a regular PC. This is not as hard as you would think, although your success/effort ratio will depend upon how closely the hardware in your PC matches that in Mac hardware - e.g. if you're running a Core 2 Duo on an Intel Motherboard, with an NVidia graphics card you are laughing. If you're running an AMD machine or something without SSE3 it gets a little more involved.
If you purchase (or already own) a version of Leopard then this is a gray area since the Leopard EULA states you may only run it on an "Apple Labeled" machine. As many point out if you stick an Apple sticker on your PC you're probably covered.
The second option is more costly. The EULA for the workstation version of Leopard prevents it from being run under emulation and as a result, there's no support in VMWare for this. Leopard server, however, CAN be run under emulation and can be used for desktop purposes. Leopard server and VMWare are expensive, however.
If you're interested in option 1) I would suggest starting at Insanelymac and reading the OSx86 sections.
I do think you should consider whether the time you will invest is going to be worth the money you will save though. It was for me because I enjoy tinkering with this type of stuff and I started during the early iPhone betas, months before their App Store became available.
Alternatively, you could pick up a low-spec Mac Mini from eBay. You don't need much horsepower to run the SDK and you can always sell it on later if you decide to stop development or buy a better Mac.
Update: You cannot create a Mac OS X Client virtual machine for OS X 10.6 and earlier. Apple does not allow these Client OSes to be virtualized. With Mac OS X 10.7 (Lion) onwards, Apple has changed its licensing agreement in regards to virtualization. Source: VMWare KnowledgeBase
For iOS 5.1.1 and lower, use the openURL method of UIApplication. It will perform the normal iPhone magical URL reinterpretation. so
[someUIApplication openURL:[NSURL URLWithString:@"http://maps.google.com/maps?q=London"]]
should invoke the Google maps app.
From iOS 6, you'll be invoking Apple's own Maps app. For this, configure an MKMapItem object with the location you want to display, and then send it the openInMapsWithLaunchOptions message. To start at the current location, try:
[[MKMapItem mapItemForCurrentLocation] openInMapsWithLaunchOptions:nil];
You'll need to be linked against MapKit for this (and it will prompt for location access, I believe).
Best Answer
As Kevin points out, URL Schemes are the only way to communicate between apps. So, no, it's not possible to launch arbitrary apps.
But it is possible to launch any app that registers a URL Scheme, whether it's Apple's, yours, or another developer's. The docs are here:
Defining a Custom URL Scheme for Your App
As for launching the phone, looks like your
tel:link needs to have least three digits before the phone will launch. So you can't just drop into the app without dialing a number.